You know the PCI-SIG might break the pattern with PCIe 5.0, just to mess with us. But for right now, Tom's Hardware seems to have acquired part of the PCIe 4.0 spec and it is expected to get 2 GB/s bandwidth per lane, per direction. This is double the bandwidth of PCIe 3.0, continuing the trend of each major PCIe release doubling bandwidth of the previous major version.

A 16-lane PCIe 4.0-compliant graphics card or storage add-in board (that feels so weird to write...) has a maximum bandwidth of 32 GB/s inbound and 32 GB/s outbound, 64 GB/s total. This is still below GDDR5 bandwidth, but approaching the same order of magnitude. That said, memory bandwidth is the major roadblock for optimizing GPGPU workloads, already. APUs will probably still have an advantage in CPU and GPU tag-teaming tasks, despite their lower compute performance.

According to bit-tech, the spec is expected to arrive with Skylake and its 100-series chipset.

Just as Intel is slowly persuading its super fast data interconnect, the PCI Special Interest Group is already introducing their own competing standard in the form of a PCI Express cable that is slated to be capable of a drool-worthy 32Gbps (gigabits per second). Planned to be constructed from copper wire, the cable standard will be launched as part of the PCI Express 3.0 standard and will be able to pipe both data and power through a thin, flattened cable up to 3 meters (9.84 feet) in length.

The PCIe cable is able to achieve this high bandwidth by combining up to four parallel lanes, each capable of 8 Gigatransfers per second (GT/s). Further, it will be able to provide approximately 20 watts of maximum power to peripheral devices. Speedy connectivity to fast SSD based portable hard drives as well as to tablet and smart phone devices for sync, additional touch interface, and external displays are all aims of the PCIe cable. It is squarely aimed to compete with Intel-backed Thunderbolt; however, the PCI SIG has not stated as such, yet. The interest group was quoted by EE Times in saying "There are solutions [like this] in the industry--Thunderbolt is one of them, and some companies are doing own thing,"

Intel's Thunderbolt and the PCIe cable will soon enter the Thunderdome to battle for supremacy

The PCIe cable is expected to be ready for peripheral device makers’ integration as early as June 2013. In the future, the cable is likely to be included in the PCI Express 4.0 standard where it will receive an upgrade to 16 GT/s lanes, and from their it will subsequently receive an upgrade to an optical based transmission material.

You can read more about the new PCI Express cable as well as its merits as a open standard (and how that affects Thunderbolt’s proprietary nature) over at EE Times.